In reply to leehawkins:
Trad does have more inherent risk and you may favour sport for the relative safety that it brings to climbing. In trad, besides gear coming out also the distance between pieces of protection can vary greatly and tends to go up as you climb through the grades and the rated breaking strain of each piece may be from 14Kn down to 2Kn depending on it's size and how it is constructed. Trad isn't just about using cams though. There are other active devices such as tricams and (sliding) ball nuts and there are many quite different forms of passive protection too which range from the very small RPs and Micro Stoppers all the way through to large hexes the size of your fist. From the starting point of already having a harness, rope, belay device, shoes and a helmet, a rack can be ready to go in about £200 - £250 and can take years to be fully added to, bit by bit.
Some people don't want the added risk and some people don't want to or are unable to afford to get the gear involved, which is fair enough.
What may be a cost for you, if you think that trad climbing is something that you would like to get into, is that after climbing only sport for say a year or two before moving to trad it may result in some disappointment about how difficult the climbs are that you can manage when you start out in trad initially. It is not uncommon for say a 6a+/6b outdoor climber to be stuck at severe or hard severe when moving into trad because the head game is more pronounced than they expected it to be. You don't have to make a decision now, but it is certainly worth considering. People stay with both disciplines exclusively as much as people crossover and do both. And if you want some inspiration then here is a video that you may not have seen from a month or two back on UKC:
http://www.ukclimbing.com/videos/play.php?i=1036
Certainly if you haven't got a helmet then spend your gri gri money on that and whatever sort of climbing you are planning on doing. Good luck and stay safe